π-Electron excess (π-electron-rich) organic molecules are used as charge transfer materials or photoconductive materials in many fields such as organic electroluminescence devices, organic light-emitting diodes, photoelectric transducers, photoconductors for electrophotography, and liquid-crystal displays. In general, the organic molecules used for such purposes have an extended π-conjugation system or assume a structure in which the planar (disk-shaped) molecules with the π-electron system stack up or pile up, so that the transfer of charge carriers (positive holes) is efficiently effected. Examples of the latter type are disk-shaped fused aromatic hydrocarbons typified by triphenylene.
It is known that triphenylene, when introduced with long chain groups, exhibits liquid crystal properties and has high conductivity for an organic molecule. This is attributed to the stacking or columnar alignment of the disk-shaped molecules, which forms the so-called “discotic” liquid crystal structure. However, computational studies reveal that triphenylene molecules in mesogenic phase will not assume the configuration in which the four benzene rings completely overlap with one another (for example, see P. Etchegoin, Phys. Rev. E, 56, 538 (1997)).
Control of the molecular configuration of disk-shaped aromatic compounds, such as triphenylene, so as to realize a molecular assembly in which π-electron systems or aromatic rings completely overlap can be expected to contribute to the development of novel functional materials with an improved charge carrier transfer property or photoconductivity. However, no such technology is available so far.
The object of the present invention is to provide novel aromatic compounds suitable for use as charge carrier transfer materials and photoconductive materials.